There is substantial literature in the art with respect to the hydrogenation of methylenedianiline to produce 4,4'-methylenedi(cyclohexylamine), also called bis(para-aminocyclohexyl)methane, and bis(4-aminocyclohexyl)methane hereinto after referred to as PACM. Some of the early work was done by Whitman and Barkdoll, et al. and their work is set forth in a series of U.S. Pat. Nos. e.g., 2,511,028; 2,606,924; 2,606,925; and 2,606,928. Basically the processes described in these patents involve the hydrogenation of methylenedianiline at pressures in excess of 200 psig, preferably in excess of 1,000 psig, at temperatures within a range of 80 to 275.degree. C. utilizing a ruthenium catalyst for the hydrogenation. The hydrogenation is carried out under liquid phase conditions and an inert organic solvent is used in the hydrogenation process. Examples of ruthenium catalysts utilized for the hydrogenation process include ruthenium oxides such as ruthenium sesquioxide and ruthenium dioxide; and ruthenium salt.
Brake, et al. continued in the manufacture of PACM by hydrogenating methylenedianiline. They found that if the ruthenium was carried upon a support and the support alkali-moderated, the catalyst was much more active and catalytically effective in producing the desired hydrogenated PACM product. Alkali moderation was effected by contacting the catalyst and support with alkali metal hydroxide or an alkoxide; also, such alkali moderation of the catalyst could be effected prior to hydrogenation or in situ during the hydrogenation. Representative patents showing the utilization of alkali moderated ruthenium catalysts to hydrogenate methylenedianiline include U.S. Pat. Nos. 3,636,108; 3,644,522; and U.S. Pat. No. 3,697,449. Alkali metal and alkaline earth metal nitrates and sulfates have similarly been shown effective in U.S. 4,448,995 under high pressure (4000 psi) hydrogenation conditions.
U.S. Pat. No. 3,959,374 discloses a process for the preparation of PACM by pretreating a mixed methylenedianiline system with a nickel containing hydrogenation catalyst prior to hydrogenation with ruthenium. The pretreatment was alleged to overcome low yields (52.4%) and long reaction associated with nickel and cobalt. Ruthenium catalysts, although commonly used for hydrogenation, were not suited for hydrogenation of a feed containing impurities, e.g. isomeric impurities. Impurities in the feed allegedly caused a rapid decline in activity and hydrogenation efficiency.
One of the early uses of PACM was for the production of various nylons and these nylons were prepared by reacting PACM with sebacic acid or adipic acid. Nylons of various quality were produced when PACM was reacted with these acids, such quality being affected by the relative concentration of the particular isomers of PACM used in the reaction. The cis,cis(m.p. 60.5-61.9.degree. C.) and especially the cis,trans(m.p. 35.7-36.9.degree. C.) geometric isomers are lower melting than the trans,trans(m.p. 64-65.4.degree. C.) isomer. When reacted with sebacic or adipic acid they, or particularly the even lower melting mixture of isomers, produce a nylon having a cloudy and opaque appearance and infusible whereas if the higher melting isomer; i.e., the trans,trans-isomer were utilized the nylon would be clear, transparent, and fusible.
U.S. Pat. Nos. 3,347,917; 3,711,550; 3,679,746; 3,155,724; 3,766,272 and British Pat. No. 1,122,609 disclose various-isomerization processes and hydrogenation processes to produce PACM containing high trans,trans-isomer content; i.e. an isomer content near equilibrium typically 50% trans,trans-, 43% cis,trans and 7% cis,cis-. As in the early work ruthenium catalysts were used to effect isomerization. This product was often called PACM-50.
Another use of PACM was in the preparation of an aliphatic isocyanate suited for forming light stable urethane coatings and lacquers. This diisocyanate was obtained from a secondary product low in trans,transisomer. This product was obtained upon separation of the more desirable trans,trans- isomer from the reaction product mixture of isomers produced by the hydrogenation of methylenedianiline in the presence of ruthenium. The secondary or residual product contained approximately 20% of the trans,trans- isomer and was referred to as PACM-20. PACM-20 exhibited utility in the manufacture of liquid isocyanates. 4,4'-Methylenedi(cyclohexylisocyanate) (H.sub.12 MDl) produced upon phosgenation of the methylenedi(cyclohexylamine) was a liquid diisocyanate stable to storage at room temperature; e.g., from 20 to 25.degree. C. ln contrast PACM-50, which contained approximately 50% trans,trans- isomer, resulted in the production of H.sub.12 MDI which was a solid at room temperature. Accordingly, for purposes of isocyanate production and further utilization in the manufacture of polyurethane formulations, PACM-20 was preferred to PACM-50 for the synthesis of the aliphatic diisocyanate.
With the growth of the polyurethane industry it has become desirable to produce substantial quantities of PACM-20 in preference to PACM-50. Allen in U.S. Pat. No. 4,394,522 and U.S. Pat. No. 4,394,523 discloses processes for producing PACM which contains the trans,trans- isomer in relatively narrow amounts e.g. from 15 to 40% and preferably less than 40% by weight. The synthesis of PACM containing less than 40% by weight of the trans,trans- isomer is achieved by carrying out the hydrogenation of MDA in the presence of unsupported ruthenium dioxide at pressures of at least 2500 psia or in the presence of ruthenium on alumina under pressures of at least 500 psia and preferably from 1500 to 4000 psia in the presence of an aliphatic alcohol and ammonia. Major disadvantages of these processes are the equipment require.d for high pressures and, as cited in U.S. Pat. No. 3,743,677, the inability to maintain high yields of such reactions when they are carried out on a commercial scale due to inadequate temperature control.
Other catalysts have been utilized for the hydrogenation of methylenedianiline and examples are shown in U.S. Pat. No. 3,591,635 and U.S. Pat. No. 3,856,862. Both disclose the use of a rhodium component as a catalytic material and each require the use of an aliphatic alcohol as a solvent. The rhodium is alkali moderated using ammonium hydroxide as a pretreatment or by carrying out the reaction in the presence of ammonia. Also, in European application 66,212 rhodium on alumina in butyl ether is disclosed to obtain 15-40% trans,trans- isomer ratio contents, but again the pressures are high (4000 psi) and the reaction times short, leading to difficult reaction product control.